Convective Outlook: Mon 16 Jul 2018
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Convective Outlook

VALID 06:00 UTC Mon 16 Jul 2018 - 05:59 UTC Tue 17 Jul 2018

ISSUED 16:29 UTC Mon 16 Jul 2018


UPDATE 16:29 UTC Cold front is a little slower than earlier expectations, and so the SLGT has been extended a little farther N + W as a result - else forecast evolution remains as outlined below

Atlantic upper trough slowly advances towards the British Isles during Monday, while a weakening surface cold front nudges eastwards across England and Wales. Strong diurnal heating ahead of the cold front will encourage the front to turn increasingly convective in nature, in an environment of 500-800 J/kg CAPE by the afternoon. Showers will develop in a rather sporadic fashion along the front (from SW England through the Midlands / E Wales to NE England) as it continues to move eastwards, some deep enough to potentially produce some lightning - but difficult to pinpoint specific areas where this is more likely than others. Have issued a low-end SLGT (ideally considered lower than 30%) to better highlight the corridor where some sporadic lightning may occur - though even here many areas may remain lightning-free.

Farther east, strong diurnal heating will result in sea breeze convergence and the development of a slack area of low pressure / surface troughing over eastern coastal counties of England. While inland dewpoints will likely mix out (into single figure Celsius in places), moisture pooling near sea breeze convergence could locally enhance dewpoints to 15-18C. If this occurs sufficiently, some 500-800 J/kg CAPE may be available which combined with breeze convergence could trigger a few (rather high-based) heavy showers during the afternoon and early evening. Forecast profiles exhibit quite dry mid/upper levels, raising some questions as to how deep convection may be able to grow and hence uncertainty over whether much lightning will occur. Main interest would be Norfolk and north Suffolk, then moving offshore.